Femoral fractures in the newborn calf: biomechanics and etiological considerations for practitioners.

The etiology of femoral fractures in calves during assisted parturition was examined from the perspective of biomechanical force analysis. Femurs were collected from newborn calf cadavers. Their physical dimensions of length, cortical thickness, and diameter were measured from radiographs, and the data were recorded. The bones were then frozen until tested. The thawed bones were compressed axially in a materials testing machine until they broke, whereupon the breaking strength of the bones at the failure site was recorded. Fracture locations were documented radiographically, and the cortical thickness and bone diameter at the fracture site were determined. Fracture configurations and locations were similar to those found in clinical cases associated with forced extraction. The breaking strength of all femurs fell within the magnitude of forces calculated to be created when mechanical devices are used to assist delivery during dystocia. An etiology based on wedging of the femur in the maternal pelvis and resulting compression during forced extraction is suggested to account for the occurrence of supracondylar fractures of the femur of calves delivered in anterior presentation using mechanical devices in a manner commonly performed by veterinarians and owners. It is recommended that care should be exercised to correct or rule out the possibility of premature engagement of the calf's stifle into the birth canal, and thereby reduce the frequency of this type of fracture occurrence in the field.